Electronic properties, layer electron transfer, metallic surfaces

It was not until recently that Chen and Goodman probed the influence of the oxide support material on the intrinsic properties at the metal surface. By covering a titania support with one or two flat atomic layers of gold they eliminated, direct adsorbate-support interactions as well as particle size and shape effects. Their results definitively showed that the electronic properties at the metal surface changed due to charge transfer between the support and the metal. Furthermore, their comparison of one- and two-layer films highlighted the dependence of these effects on the thickness of the metal slab. 

A critical problem with adhesion layers arises from grain boundary diffusion. Deposited films tend to be polycrystalline and granular. The electrochemistry of the adhesion film is frequently much less desirable than the electrochemistry of the primary film. Moreover, minute contamination of the primary metal film surface by adhesion components can dramatically degrade the electron transfer properties (e.g., electrochemical reversibility, as evidenced by cyclic voltammetric peak potential separation) of the film [58], Thus it is essential that the adhesion layer is not exposed to solution. While the rate of diffusion of adhesion metals through the bulk of the primary layer is quite slow, grain boundary diffusion along the surfaces of grains is much faster. In many cases, the adhesion layer can seriously compromise the performance of the electrode. This is particularly a problem for chromium underlayers. Recently a codeposited Ti/W adhesion layer has been recommended as an alternative to chromium, with reportedly better adhesion and fewer interferences than Cr. A procedure was also described to recondition these electrodes to minimize interference by adhesion layer metals [58]. 

The mechanism for the perturbation of the fluorescence properties of the monolayers by the metal ions is not well understood yet. The type of ligating functionality and its distribution across the layer, together with possible steric constraints or additional surface interactions, such as monolayer packing, van der Waals forces, and cation-jr, and jr-ir interactions, may determine the properties of the layers, and therefore the response toward different metal ions. Cation-controlled photoinduced processes, such as photoinduced electron transfer and charge transfer, may be responsible for the fluorescence perturbation.45... 

The electric field across electrochemical interfaces is of key importance to understanding electrochemical processes. The barrier heights for the charge transfer processes at such interfaces depend on the field, which in turn depends on the overall electronic properties of the interface. To understand the effect of the field on these barriers requires quantitative insight into the electronic structure of the interface. Theoretical treatments of the physics of electrochemical interfaces are needed. These must handle more effectively such questions as the role of electronic surface states and the interactions of the solvent and ions of the compact double layer with the metal orbitals, as well as the spillover of the conduction band electrons into the interface. The experimental techniques described in the previous section of this chapter will exert a significant influence on the development of such understanding, but this will require the combined efforts of theorists and experimentalists. 

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